整百年份是闰年的为什么是４００的倍数○冯惠洲在九年义务教育小学五年制第六册数学教材的年、月、日这一节中，当遇到公历年份是整百数时如何判断平、闰年，教材中专门加了底注：“公历年份是整百年数的必须是４００的倍数才是闰年”。有的学生就追问这是为什么？就这个... Why the whole year is a hundred year leap year is a multiple of 400 ○ Feng Huizhou in the nine-year compulsory primary school sixth year mathematics textbooks in the year, month, day of this section, when the calendar year is the whole hundred how to judge Flat, leap year, textbooks added a special note at the end: “Gregorian calendar year is a whole hundred years must be a multiple of 400 is a leap year.” Some students to ask why this is? this one...